Seasonal Influenza Fever – Causes, Prevention, Treatment

Image courtesy of Mikael Häggström, some rights reserved.

Influenza is a respiratory tract infection caused by the influenza virus which is an orthomyxo virus. Influenza is a highly contagious infection transmitted by droplets. Total three types of influenza viruses are found – Type A, Type B, Type C. Type A influenza virus can infect birds and humans but Type B and C infects only humans.


Symptoms of influenza virus are variable, sometimes it is asymptomatic, sometimes systemic symptoms also occur. Type C influenza virus causes mild illness. Symptoms of influenza virus include fever, chills, malaise, headache, body ache, rhinorrhoea. Respiratory symptoms include rhinorrhoea, sore throat, cough and hoarseness of voice. Children may suffer from gastrointestinal symptoms like nausea, vomiting or loose stool. Symptoms may persist for seven days. The majority of influenza fever symptoms are similar to other viral fever. Influenza can cause neurological symptoms in children, though it occurs rarely. Neurological symptoms may include seizure disorders. behavioral changes or confusion. Reye’s syndrome may occur when an influenza-infected child takes aspirin for fever control.


This viral infection can be detected by many laboratory investigations. Nowadays sensitive tests like PCR ( Polymerase Chain Reaction ) are available. Nasopharyngeal swab, Oropharyngeal swab, nasal aspirate or sample of bronchoalveolar lavage are sent for microbiological test for influenza virus strain detection. Though rapid diagnostic kits are highly specific, their sensitivity is low, Often gives false-negative results. Influenza virus-induced pneumonia can be detected by the RT-PCR test. Blood count reveals reduced leukocyte count during influenza virus infection.


Influenza fever often gets complicated and resulting in the hospitalization of the patient. Complications of influenza fever include pneumonia, hypoxemia, secondary bacterial infection even shock. Elderly persons and children are more prone to develop complications. Obese persons or persons with other co-morbid conditions like diabetes, COPD, asthma, hepatic disease, renal disease, neurological disorder or immune Compromised are also susceptible to influenza complications.


Complications of seasonal influenza fever during pregnancy can be fatal for both mother and fetus. It leads to severe illness, respiratory failure distress. Staphylococci, streptococci and Haemophilus cause secondary bacterial inflection as influenza virus destroyed respiratory epithelium. Neurological complications are rare.


Treatment of influenza fever is of 2 types

  • Supportive therapy b specific antiviral therapy.
  • SUPPORTIVE THERAPY – Supportive therapy is given for symptomatic relief of viral infection. Acetaminophen is given for fever and myalgia control. Antihistamines like levocetirizine, Desloratadine are used to control rhinorrhoea. Levosalbutamol syrup can be given for colon treatment.
  • SPECIFIC ANTIVIRAL TREATMENT – Before starting specific antiviral therapy for seasonal influenza fever, a diagnosis must be confirmed by the microbiological and serological investigation. Early diagnosis and treatment are necessary for the prevention of influenza complications. Antiviral therapy should be started as soon as possible to reduce symptoms and complications. Laboratory confirmed influenza fever gets a quick recovery on early initiation of specific treatment. It also reduces the chances of hospitalization. Previously amantadine and rimantadine are used for type influenza but these drugs gradually become resistant especially for H1N1 and H3 N1 strains. At present newer antiviral drugs belong to neuraminidase inhibitor groups are most effective for influenza A and influenza B virus. Oseltamivir, Zanamivir and peramivir are FDA approved neuraminidase inhibitors oseltamivir is the drug of choice for influenza fever. Oseltamivir is given orally 75mg twice daily for 5 days. It can be used during pregnancy also. Zanamivir is given in inhalation route 10 mg. Zanamivir is given 2 inhalations twice daily for 5 days. This drug should not be used in asthma patients for increased risk of bronchospasm.

Peramivir is given as an intravenous injection 600mg single dose in case of oseltamivir intolerance. The efficacy of peramivir is low in comparison to oral oseltamivir.

NNRTI (Non-Nucleoside Reverse Transcriptase Inhibitor) drug dapivirine is an antiviral drug is found to be useful for influenza A and B viruses.


For influenza prevention, the influenza vaccine is the best method. The influenza vaccine is taken yearly for the prevention of influenza and its complications. Trivalent or quadrivalent vaccines are available in the market. The trivalent vaccine contains antigens from 2 strains of influenza A (H1N1, H3N2)and one strain of influenza B. Quadrivalent vaccines include an extra influenza B strain along with the strains of a trivalent vaccine. Influenza vaccines can be given to all adults above the age of 18 including pregnant women also. Influenza vaccine should not be given to persons with the previous history of allergy to influenza vaccine for allergy to egg.

Antiviral chemoprophylaxis is also used to prevent influenza infections chemoprophylaxis has an 80% protection rate.

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